Formación

DHW + PV: solar PV top-up for domestic hot water

DHW + PV: all-electric hot water heating for Passive houses, with surplus solar PV top-up Energy consumption from DHW use is often higher than heating and cooling requirements in a residential Passivhaus. This is mainly due to the large losses inherent in storing and recirculating hot water, and because heating and cooling demands are very low, thanks to an optimised fabric design that …

DHW + PV: all-electric hot water heating for Passive houses, with surplus solar PV top-up

Energy consumption from DHW use is often higher than heating and cooling requirements in a residential Passivhaus. This is mainly due to the large losses inherent in storing and recirculating hot water, and because heating and cooling demands are very low, thanks to an optimised fabric design that minimises thermal losses/gains. Reducing the net energy consumption of DHW in Passivhaus is therefore important.  

The article presents monitored data from a solar PV installation for a single-family certified Passivhaus in Girona, Spain, designed by Tigges Architekt and Energiehaus Arquitectos, with services installed by Progetic (Figure 1 & Figure 2). The system diverts surplus PV production to an electric immersion heater in the DHW tank, where the primary generator for hot water is an air-source heat pump.  

Figure 1: View of the south façade of the case study home [Source: Loxone]
Figure 2: View of the east façade of the case study home [Source: Loxone]

The first step is always to optimise DHW system design and reduce losses. The second step is to find simple and low-maintenance solutions for on-site renewable energy generation for DHW production. The solution implemented here is an all-electric system that reduces net hot water energy consumption, using a solar PV array to top up hot water production, with an air-source heat pump as the main hot water generator. The system avoids the maintenance problems found in solar thermal systems that are susceptible to overheating in summer months when occupants are away, where fluid dry-up in the primary circuit between panel and tank is a frequent cause of failure. 

A series of calculations were done with the PHPP tool, to determine useful energy demands, final energy consumption and projected energy bills, by category. For the calculation of the energy bill, the weighted price of electricity was calculated at € 0.21 / kWh. Additionally, an analysis of DHW demand and losses by category was made. Figure 3, Figure 4, Figure 5 and Figure 6 show the results. 

DHW consumption appears as the second highest energy consumer, 34% of the total. If we look at DHW demand and losses, only 33% is due to heating hot water, the remaining 67% are losses, of which 44% are due to recirculation, 18% due to individual pipes, and a 5% for storage. The total predicted final energy consumption for DHW is 1,764 kWh, an average of 147 kWh/month. 

Figure 3: Useful energy demands, final energy consuption and costs, by category, calculated with PHPP
Figure 4: Final energy consumption by category and energy costs, calculated with PHPP
Figure 5: DHW demand and losses, calculated with PHPP
Figura 6: DHW demand and losses, calculated with PHPP

System

The system incorporates a PV array with 12 polycrystalline modules and a peak power of 3.18 kWp (Figure 7), and a 3 kW inverter. The main hot water generator is a 6 kW ait-to-water heat pump (wich also supplies heating and cooling, with a 500-liter DHW tank and 3-kW electrical immersion heater (Figure 8). DHW production is isntantaneous. When the sun is shining and there is more PV generation than electrical consumption in the home, a control system diverts the electrical energy from the PV panels that cannot be self-consumed into thermal energy in the DHW tank for use in the afternoon or evening (Figure 9).

Figure 7: 3,18 kWp roof-mounted PV array
Figure 8: DHW
Figure 9: Control system

This is particularly interesting in the summer in passive houses in warm climates with active cooling and only one heat pump, as it generally allows the heat pump to keep itself in cooling mode, rather than stopping, reversing and going into hot water heating mode, before reverting back to cooling (for example, when occupants return home in the afternoon and shower etc). The hysteresis in this process can mean the home is without active cooling during 2/3 hours, which can be a problem in comfort terms. The control system monitors the home’s electricity consumption and PV production, sending surplus electricity to the resistance in the DHW tank. The power of the resistance heater is modulated through a voltage regulator, due to the fact that the output power of the photovoltaic generator varies continuously according to the level of solar radiation, and that the available surplus depends on the transient electricity consumption of the house. 

Monitoring data & conclusions

Monitoring data for 2018-2019 shows a total of 1211 kWh of PV production was diverted to the electrical resistance in the DHW tank, with a peak water temperature of 58 ºC. PHPP calculations projected that DHW consumption was 1764 kWh. Logically, not all of the PV energy diverted to the DHW tank is useful, as it depends on when DHW consumption takes place. Nonetheless, the system shows that solar PV top-up is effective for assisting in hot water generation, thereby reducing net energy consumption derived from hot water use, shown in (Figure 10) and (Figure 11) below.

Figure 10: Monitored data showing PV generation, solar PV DHW production, and total energy consumption, 1-8 June 2019
Figure 11: Monitored data showing PV generation, solar PV DHW production, and total energy consumption, 5 June 2019

Bibliography

[1] Feist W., Peper S., 2015, “Energy efficiency of the Passive House Standard: Expectations confirmed by measurements in practice”. Passive House Institute Dr. Wolfgang Feist, Rheinstraße 44/46, 64283 Darmstadt, Alemania.

[2] Grant N., Clarke A., 2010, “The importance of hot water system design in the Passivhaus”. Elemental Solutions, Withy Cottage, Little Hill, Orcop, Hereford, HR2 8SE, Reino Unido.

[3] Parlamento Europeo, 2010, “DIRECTIVA 2010/31/UE DEL PARLAMENTO EUROPEO Y DEL CONSEJO, de 19 de mayo de 2010 relativa a la eficiencia energética de los edificiosb(refundición)”.

Hygrothermal calculation of a bio-based timber frame wall module

Hygrothermal calculation of a bio-based timber frame wall module Dynamic hygrothermal simulation and full-scale validation of a structural insulated panel made from bio-based materials. Given the environmental impact of the construction sector- responsible for 40% of the total primary energy consumption of the European Union- reducing both the embodied energy of materials at manufacturing stage …

Hygrothermal calculation of a bio-based timber frame wall module

Dynamic hygrothermal simulation and full-scale validation of a structural insulated panel made from bio-based materials.

Given the environmental impact of the construction sector- responsible for 40% of the total primary energy consumption of the European Union- reducing both the embodied energy of materials at manufacturing stage and minimising operational energy consumption in buildings are urgent tasks. Timber, agricultural residues, and bio-based materials are local renewable resources that can be transformed into buildings products and components, fomenting the creation of circular economies, and reducing the environmental impact of the sector. The objective of the European ISOBIO project, that ran from 2015 to 2019, financed under the Horizon2020 program, was to address these problems through the development of new insulating materials and renders from plant fibres, agricultural residues, and bio-based binders. The article presents the results of dynamic hygrothermal simulations and full-scale validation of a structural insulated panel made from bio-based materials, for use in the construction of nearly-zero energy buildings.

ISOBIO structural insulated panel for new buildings

The prototype panel measured 1.95m x 1.95m, with a total thickness of 33.2cm in 8 layers with 9 different materials (Figure 1). The panel was rendered external with 25mm of lime and hemp plaster, applied on a rigid 50mm hemp insulation board, mechanically fixed to a 145mm red pine timber structure, filled with hemp, cotton, and flax insulation, followed by a 12mm OSB 3 timber board. An airtight and dynamic vapour control membrane was fixed to the inner face of the OSB, followed by a 45mm service void, insulated between timber battens with hemp, cotton, and flax insulation. The battens were positioned at 90º in relation to the main structural joists to reduce the thermal bridging through the timber. The inner service void was lined with a 40mm thermo-compressed straw board, plastered on the inside with 15mm of composite clay-hemp plaster, applied in 3 layers.

Figure 1: ISOBIO panel section drawings and materials
Figure 2: Location and type of sensros installed in the panel
Figure 3: Panel installation at the HIVE demonstrator, Wroughton, UK

Test set-up

Figure 3 shows the installation of the panels in the demonstrator in Wroughton, UK. A monitoring system was installed, with a meteorological station recording external climate conditions: dry air temperature, relative humidity, solar radiation, wind speed, wind direction, rainfall, and barometric pressure. A temperature probe was installed on the outside of the panel, with a heat flow and temperature probe on the inner face, for measuring thermal transmittance in accordance with ISO 9869 [1]. In addition, temperature and relative humidity sensors were installed at 3 positions within the panel (Figure 2), to measure transient hygrothermal behaviour inside the panel and compare the results with dynamic hygrothermal simulations made with the WUFI Pro tool, following EN 15026 [2]. WUFI Pro 1D is a tool developed by the Fraunhofer Institute in Germany for assessing the hygrothermal performance of one-dimensional building envelope cross-sections, taking into account the moisture content of the materials, their transient hygrothermal performance, capillary transport and summer condensation, with hourly outdoor climate conditions. The software version used was WUFI Pro v. 6.2.1.2210

Data was measured at an interval of 5 minutes, from 24/02/2018 to 14/03/2018 in the HIVE demonstrator, UK, for a total 432 hours, or 18 days, with 5184 data points. The interior temperature was maintained at an average of 25.5 °C throughout the period, with the use of an electric convection heater.

Monitoring Results and Validation

Figure 4 shows a cross section of the modelled panel, with sensor locations. Figure 5 shows the WUFI model of the panel and corresponding sensor locations.

Figure 4: Cross section of panel and sensor locations
Figure 5: Cross section of WUFI model and sensor locations

Figure 6 shows measured and modelled temperature and RH at position 2 (between the CAVAC rigid insulation and Biofib Trio insulation). Temperature dynamics are well reflected in the model. RH dynamics are less well reflected.

Figure 6: Measured vs. modelled (WUFI) interstitial temperature and relative humidity, positin 2, ISOBIO new-build panel, HIVE demonstrator

Figure 7 shows the measured and modelled temperature at position 3 (between the Biofib Trio insulation and OSB board). Temperature dynamics are well reflected in the model, with RH less so. The model nonetheless shows very close alignment with measured results.

Figure 7: Measured vs. modelled (WUFI) interstitial temperature and relative humidity, position 3, ISOBIO new build panel, HIVE demonstrator

Figure 8 shows the measured and modelled temperature and RH at position 4 (between the Intello membrane and the Biofib Trio insulation). Temperature and RH dynamics are well reflected in the model.

Figure 8: Measured vs. modelled (WUFI) interstitial temperature and relative humidity, position 4, ISOBIO new-build panel, HIVE demonstrator

Figure 9 shows the measured average heat flow rate, compared with the WUFI modelled heat flow rate, showing very good agreement.

Figure 9: Measured vs. modelled (WUFI)average heat flow rate, ISOBIO new-build panel, HIVE demonstrator

Conclusion

The results of the measured and modelled temperature and RH show good correlation, with dynamic temperature variations accurately reflected in the model. The short-term variations in relative humidity are not reflected with the same precision in the WUFI modelling results, possibly due to the assumption that the equilibrium water content in the materials is instantaneous, where in reality, there is hysteresis [3]. The hourly measured and modelled thermal transmittance data show very good correlation, with a difference of only 4% over the monitoring period.

The results indicate that bio-based materials combined in a composite SIP panel of this type can offer predictable hygrothermal performance for use in nearly-zero energy buildings.

References

  • ISO 9869-1:2014 Thermal Insulation – Building elements – in-situ measurement of thermal resistance and thermal transmittance. (Aislamiento térmica – elementos constructivos – medición in-situ de la resistencia térmica y transmitancia térmica)
  • UNE-EN 15026:2007, Comportamiento higrotérmico de componentes de edificios y elementos constructivos. Evaluación de la transferencia de humedad mediante simulación numérica.(Ratificada por AENOR en junio de 2010.)
  • N. Reuge, F. Collet, S. Pretot, S. Moisette, M. Bart, O. Style, A. Shea, C. Lanos 2019, Hygrothermal transfers through a bio-based multilayered ISOBIO wall – Part I: Validation of a local kinetics model of sorption and simulations of the HIVE demonstrator. Laboratoire de Génie Civil et Génie Mécanique, Axe Ecomatériaux pour la construction, Université de Rennes, 3 rue du Clos Courtel, BP 90422, 35704 Rennes, France.

Healthy home: materials and indoor air quality

The U.S. EPA (Environmental Protection Agency) estimates that the air in our homes is 2 to 5 times more polluted than outdoor air. After spending so much time at home during successive COVID lockdowns, the importance of living in a healthy home has perhaps become clearer than ever before.

Healthy home: materials and indoor air quality

Materiales y calidad del aire, claves para los espacios saludables
Figure 1: Example of materials that can affect a home’s indoor air quality [Source: Jose Hevia / H.A.U.S]

The U.S. EPA (Environmental Protection Agency) estimates that the air in our homes is 2 to 5 times more polluted than outdoor air. After spending so much time at home during successive COVID lockdowns, the importance of living in a healthy home has perhaps become clearer than ever before.

What kind of environmental conditions are we looking for in a healthy home? Operative or comfort temperatures of between 20 ºC – 25ºC, relative humidity between 40 % – 60%, and surface temperatures ≤ 3ºC of the indoor air temperature.  With an indoor air temperature of 20ºC and a relative humidity of 50%, interior surfaces need to be ≥ 13ºC to prevent the risk of mould growth, and ≥ 9ºC to avoid surface condensation. Exposure to mould spores can cause health issues such as eye, skin and throat irritation, nasal stuffiness, coughing and wheezing. Alongside healthy thermal conditions, good indoor air quality is key for wellbeing, solved largely by good ventilation, but also by preventing the entrance of outdoor contaminants (such as particulate matter, radon gas etc.) and by reducing the generation of indoor contaminants due to emissions from materials, furniture, and finishes.

If continuous and controlled ventilation is key, we need to get to the root of the problem: to reduce and avoid materials that emit toxic chemicals in our home. In this article Oliver Style explains what to be on the lookout for, and presents three certification systems that are useful for choosing healthy products and materials.

What does indoor air contain?

To live in a healthy environment, we need to look at the products, materials and furniture we have in our home, since we breathe the particles they emit and we are often in direct physical contact with them.

The first step is to choose paints, varnishes, timber, ceramics, textiles, and furniture with a very low emissions of Volatile Organic Compounds (VOCs). VOCs are of both natural and artificial origin. They all share the common characteristic that they are made of carbon and other elements such as hydrogen, halogens, oxygen, or sulphur. They are present in solids or liquids and are either volatile or occur in a gaseous state at room temperature, which means they move quickly around indoor spaces. Some of them modify the chemical composition of their local environment and are harmful to our health.

Formaldehyde, a colourless, volatile, and toxic gas (classified as carcinogenic by the EU), and other VOCs, are often found in paints, paint strippers, wood preservatives, wood products, binders, glues, waxes, plastics, pesticides, aerosols, synthetic carpets, cleaning products, disinfection products and degreasers. Health effects include asthma, eye, nose and throat irritation, headaches, loss of coordination, nausea, liver, kidney and central nervous system damage. VOCs can be endocrine disruptors and cause respiratory and hormonal diseases, prolonged sleep and behavioural disorders, reproductive disorders and foetal development, cancer, and multiple chemical sensitivity (MCS).

Another harmful component to pay close attention to is particulate matter (PM)- fine particles and fibres with a diameter of 10 micrometres (PM10) or less (PM2.5 and PM 1). PM2.5 particles can reach the lungs, and PM1 can reach the bloodstream. Short and long-term exposure to these particles is associated with cardiovascular and respiratory diseases, including lung cancer. These diseases become more evident when the fibres come from highly toxic materials such as asbestos.

Which are the best materials and products to use in our home?

To avoid and minimize harmful substances inside the home, it’s best to look for products that have been modified or processed as little as possible, made with low-emission paints, varnishes, and glues, formaldehyde free, and if possible, certification for low emissions. Three such certification systems are mentioned below, which classify materials and products and quantify their harmful emissions.

Linoleum or solid wood floors are recommended because they usually contain few adhesives and generally have low emissions. Anything that has been varnished or coated in a controlled factory environment (rather than on-site) will lead to lower emissions in the home. If you use laminated timber flooring, look for one that is free of formaldehyde.

Carpets are in generally not advisable, as they end up collecting all kinds of particles, and in some cases, contain volatile coal ash or polyurethane laminates. Natural fibre carpets are recommended.

Furniture and wood composite products can be a significant source of emissions because they are often made with urea-formaldehyde adhesives. Look for solid wood or plywood furniture, free of formaldehydes. 

As far as kitchen counters go, natural rock is a good option, such as quartz. Alternatively, look for Corian (a synthetic material for solid surfaces composed of acrylic resin and aluminium hydroxide).

As for thermal insulation, exposure to sprayed foam insulation containing isocyanates can cause asthma. If you use fiberglass or mineral wool insulation, make sure it’s formaldehyde free. In general, bio-based or mineral insulation are the healthiest options.

Be careful: products are sometimes sold as “ecological” due to their recycled content, but they can be harmful to your health. For example, some ceramic tiles are made with recycled glass from cathode ray tubes from old TVs, which are considered hazardous waste due to their high lead content.

Emissions & materials: certification systems

1. French certification for indoor air emissions

Emisiones Dans l’air intérieur
Figure 2: Example of the indoor air emissions certification, with A+ product rating

The label “Émissions dans l’air interieur” classifies building materials, furniture and finishing products marketed in France, being mandatory for all products sold there. The certification classifies products according to VOC emissions, from A+ to C (A+ being lowest emissions), according to the ISO 16000 standard. If a product exceeds the limits, it cannot be sold (admittedly “C” class is not very demanding…). The following emissions are evaluated:

  • Formaldehyde
  • Acetaldehydes
  • Toluene
  • Trichloroethylene
  • Xylenes
  • 1, 2, 4 Trimethylbenzene
  • 1, 4 Dichlorobenzene
  • Ethylbenzene
  • 2 Butoxyethanol
  • Estriol

2. Baubiologie Rosenheim Institute certification

Geprüft und empfohlen
Figure 3: IBR Certificate Seal

The IBR, Institute for Biologically Sound Construction, is a German institution that certifies healthy and environmentally sustainable consumer construction products, and includes a series of tests that measure the emissions of a product, including:

  • Radioactivity
  • Biocides
  • Polychlorinated biphenyls
  • Heavy metals
  • VOC
  • Formaldehydes
  • Biological compatibility
  • Electrostatics

3. Eurofins Indoor Air Comfort certification

Eurofins

This certification systems classifies construction products into two categories: Standard level “Indoor Air Comfort – certified product”, which shows compliance with product emissions criteria established by EU authorities, and Higher level “Indoor Air Comfort GOLD – certified product”, which shows additional compliance for product emissions with the criteria set by the most relevant ecolabels and sustainable building organisations in the EU.

MICA Wall indoor air quality sensor
Figure 5: MICA Wall indoor air quality sensor

What you don’t measure you can’t improve

There are several testing laboratories in Spain for the measurement and certification of materials and their VOC emissions, such as Tecnalia, and SGS. What if I want to measure the indoor air quality of my home without spending a fortune? There’s affordable equipment with reasonable accuracy, such as the range of MICA sensors, manufactured by Inbiot. They measure VOC’s, formaldehydes, ozone, suspended particles, radon gas, CO2, temperature and relative humidity.

The following figure shows measured data from a MICA sensor of formaldehyde concentration in a bedroom over the course of a week.

According to the technical standard of measurement in Baubiologie SBM2015 for rest areas, values above 100 μg/m3 are already extremely significant. “The search for emission sources is a bit like looking for a needle in haystack, based on the data and measurements. But you can gradually discard sources until you find the culprit” says Maria Figols, Project Manager at InBiot.

Figure 6: Formaldehyde concentration measured in a bedroom for one week in December 2019

Better living with less emissions

Creating healthy indoor environments is clearly on the agenda, with the construction sector on centre stage. Choosing the right low-emission materials will improve indoor air quality and can help reduce illness for occupants, in the short, medium, and long term. Using products with some of the certification systems shown above is a good place to start. Alongside emissions, these kind of certification systems also assess the environmental impact of a product, making sure they don’t pose a significant hazard during manufacturing, deconstruction, recycling or waste treatment phases. Reducing the source of indoor contaminants should always be the first step. The second step- and equally important- is controlled and efficient ventilation.

Acknowledgements

To Maria Figols and Xabi Alaez from InBiot for their contributions.

Bibliography

[1] Guía Edificios y Salud, Siete Llaves para un edificio saludable. García de Frutos, Daniel et al. Consejo General de la Arquitectura Técnica de España, Consejo General de Colegios de Médicos. Enero 2020.

[2] Monitorización de vivienda de alta eficiencia, 30 Marzo 2020. InBiot. https://wiki.inbiot.es/monitorizacion-de-vivienda-de-alta-eficiencia/

Keys to the Passivhaus standard: what is it and how to achieve it?

The Passivhaus standard is a voluntary energy certification standard for new and retrofitted buildings, aimed at providing maximum comfort for occupants, excellent indoor air quality and near-zero energy consumption.

Keys to the Passivhaus standard: what is it and how to achieve it?

The Passivhaus standard is a voluntary energy certification standard for new and retrofitted buildings, aimed at providing maximum comfort for occupants, excellent indoor air quality and near-zero energy consumption. It was developed in the 90’s by the Passivhaus Institute in Darmstadt Germany, and it has since been expanding across the globe. The current climate crisis is increasingly bringing the standard into the limelight due to its radical no-nonsense approach, rooted in buildings physics, a rigorous design process and an emphasis on proper site supervision and commissioning. The objective is to close the so-called “performance gap” (where buildings fail to perform as predicted), making them fit for purpose, comfortable, healthy, and resilient. A Passivhaus building typically consumes up to 90 % less energy than a conventional building.

This article, written by Oliver Style, explains some of the key aspects of the Passivhaus and what you need to do, to achieve certification.

Las claves de la certificación Passivhaus
Figure 1: Passivhaus certification plaque [Source: Álvaro Martínez]

Passivhaus: the Basic Principles

It is often said that the standard is based on the following 5 principles:

  • High levels of thermal insulation
  • High performance windows
  • Efficient mechanical ventilation with heat recovery
  • Air tightness
  • Absence of thermal bridges

Although this simplification can make it easier to understand what Passivhaus is all about, a Passivhaus building requires a holistic design process where the whole is more than the sum of the parts… and there are many parts. So, beyond the 5 basic principles, there are several other factors that are important for achieving certification and making sure a building does what it says on the tin, especially in warm climates, namely:

  • External shading devices to reduce solar gains and avoid summer overheating 
  • Efficient Domestic Hot Water (DHW) systems, equipment and lighting: to reduce primary energy consumption and reduce internal heat gains in summer (helping avoid summer overheating).
  • Efficient heating and cooling installations
  • In climates with sufficiently low minimum night time temperatures: Natural night ventilation combined with thermal inertia, to remove heat from the building without relying only on active cooling.
Figure 2: Global temperature change relative to 1850 - 1900 [Source: IPCC Special Report 2018]
Figure 2: Global temperature change relative to 1850 – 1900 [Source: IPCC Special Report 2018]

A building designed to have very low heat losses in winter, will also keep heat out in the summer: if you fill a vacuum flask with cold water in the summer, the water will stay cool for longer than if you just left it in outside in ambient warm air.  However, once the heat is inside, it will logically dissipate more slowly due to the high level of thermal protection. That is why it’s particularly important to go beyond the “5 principles” if you want to avoid overheating problems, which will increasingly become an issue as summers get warmer due to global warming (Figure 2).

Figure 3: Passivhaus certification criteria for new construction [Source: Passive House Institute 2016] [1]
Figure 3: Passivhaus certification criteria for new construction [Source: Passive House Institute 2016] [1]
Figure 4: Passivhaus certification classes [Source: Passive House Institute]
Figure 4: Passivhaus certification classes [Source: Passive House Institute]
Figure 5: Passivhaus Low Energy Demand certification criteria [Source: Passive House Institute 2016] [1]
Figure 5: Passivhaus Low Energy Demand certification criteria [Source: Passive House Institute 2016] [1]

PHPP: “Passive House Planning Package”

For the design of a Passivhaus building, the PHPP (“Passive House Planning Package”) tool is used, a quasi-steady-state single zone energy modelling program, based on a series of spreadsheets in Excel, that provides monthly and annual energy balances. The algorithms in the tool are based on a number of ISO standards, mainly in the monthly method of EN ISO 13790, now replaced by ISO 52016 0.

The PHPP has been calibrated with thermodynamic simulations carried on with the DYNBIL tool, developed by the Passivhaus Institute, itself calibrated by extensive validations with monitored data.

PHPP stands out for its simplicity compared to dynamic tools and can be used to model (albeit in a simplified way) a wide variety of active and passive systems, at a very affordable price. The results indicate the energy balance of the building in both summer and winter, yielding results of heating and cooling demands and total and final and primary energy consumption. Although a dynamic tool is- in principle- more accurate, the large number of parameters and input data increases the possibility of modelling errors and requires experience and time for accurate use. In energy simulation, it is sometimes better to be approximately correct than precisely wrong…

Passivhaus for new build

The Passivhaus standard for new buildings is performance based: i.e., it doesn’t limit thermal transmittance values ​​of the different construction elements, but establishes maximum energy demands and energy consumption, calculated with the PHPP. The air infiltration level cannot exceed 0,6 air changes per hour (ACH) at a pressure difference of 50 Pascals, measured with an on-site test, known as the “Blower Door” test.

The limiting values for heating and cooling demands and total primary energy consumption, are shown in Figure 3.

There are 3 classes of certification: Classic, Plus and Premium. Classic does not have renewable energy generation. To get to Plus, you have to generate ≥ 60 kWh/m2·a of renewable energy (references to the building’s footprint)- typically at least as much as what the building consumes. To reach Premium, the building must generate ≥ 120 kWh/m2·a (or 4-5 times more than what the building consumes). This is shown in Figure 4. The advantage of this approach is that energy demands are reduced first, before considering on-site generation of renewable energy. This differs from the conventional net-zero energy approach, which inevitably favours buildings with very large roofs on which a large solar PV generator can be installed, leading to buildings with a poor form factor (the ratio of enclosed envelope area to useful floor area), higher losses and where on-site renewable energy generation is prioritised over reducing energy use.

PHI Low Energy Building

If the above requirements are not met, a building can be certified as PHI Low Energy Building, complying with less stringent requirements, shown below in Figure 5.

Passivhaus for retrofitting: EnerPHit

For the retrofitting of existing buildings, there is the EnerPHit seal, which offers two ways to achieve certification:

  • EnerPHit, Demand Method: performance based, with the requirements shown in Figure 6
  • EnerPHit, Component Method: prescriptive, with the requirements shown in Figure 7

For both methods, an air tightness test result of N50 ≤ 1.0 ach must be obtained. The Classic, Plus and Premium classes are also applicable to the EnerPHit standard.

Figure 7: EnerPHit Certification Criteria, Component Method. [Source: Passive House Institute 2016] [1]
Figure 7: EnerPHit Certification Criteria, Component Method. [Source: Passive House Institute 2016] [1]
Figure 6: EnerPHit Certification Criteria, Demand Method. [Source: Passive House Institute 2016] [1]
Figure 6: EnerPHit Certification Criteria, Demand Method. [Source: Passive House Institute 2016] [1]

Overheating risk in summer

For certification, overheating risk is assessed through one of the two following methods:

  • With active cooling: the limiting total cooling demand must be met (sensible + dehumidification), calculated with the PHPP, with mechanical systems capable of maintaining thermal comfort at all times (according to ISO 7730), with an operating temperature ≤ 25 ºC and a maximum of 10% of the hours in the year with an absolute indoor humidity ≥ 12 g/kg dry air.
  • With passive cooling:  the maximum overheating frequency must be met, calculated with the PHPP, with a maximum of 10% of the hours in the year with an indoor operating temperature > 25 ºC.
Figure 8: Overheating frequency classification [Source: adapted by Jessica Grove-Smith, Passive House Institute]
Figure 9: Graph showing the modification of the summer temperature of the PHPP climate data, from the "Summer Temperature Tool"
Figure 9: Graph showing the modification of the summer temperature of the PHPP climate data, from the “Summer Temperature Tool”

In the case of passive cooling, it is important to stress that 10% of the hours of the year are a total of 876 hours with an indoor operative temperature above 25 °C (the whole month of August, for example). Therefore, the recommendation is not to exceed 5%, with a good design objective being 2 – 5%, shown in Figure 8.

To reduce the risk of overheating where no active cooling is available, it is important to perform stress tests of extreme climate situations with the PHPP. For this purpose, Jessica Grove-Smith of the Passivhaus Institute has developed theSummer temperature tool[2], which adjusts the summer temperatures in the PHPP climate file, taking into account the urban heat island effect and the increase in temperatures according to IPCC’s predictions (Figure 9). This feature will be integrated directly into PHPP version 10.

For tertiary buildings and/or buildings with areas exposed to very different indoor and outdoor conditions, it is advisable to accompany the PHPP calculation (a single zone tool) with a dynamic multi-zone calculation, to analyse specific zones that may be more susceptible to overheating (for example, the top floors in a tall building with west-facing glazing).

Additionally, if the building does not have an active cooling system, it is important to test assumptions regarding user behaviour, for example, in relation to closing blinds and opening windows at night for natural ventilation. Is it realistic to think that a person will sleep all night with the blinds open, all windows fully open, and all interior doors open? It is more likely that occupants will close the blinds before going to sleep so the sun light doesn’t wake them up in the morning. If you live in an urban area, you might want to close all windows facing the street to avoid noise. All this reduces natural night ventilation flow rates and the amount of heat that can be extracted from the building.

Although the goal is always to reduce dependence on active systems to maintain comfort, in most cases, some active cooling in summer is advisable. Fortunately, the summer is also the time when there is the most solar radiation, which means active cooling energy consumption can be directly off set with on-site renewable energy production.

Air tightness: the “Blower Door” test

Central to the Passivhaus standard is the “Blower Door” airtightness test, that measures air infiltration through a piece of equipment that pressurizes and depressurizes the building. Preliminary tests must be carried out before the interior finishes are completed (to detect and correct leaks, if found), together with a final test, according to the EN 13829 [3].

The “Blower Door” test is a clear indicator of build quality. What are the advantages of reducing air leaks?

  • Reduces energy losses and heating bills in the winter
  • Reduces the entrance of moisture in warm-humid climates, thereby reducing dehumidification cooling consumption and cooling energy bills
  • Improves comfort, eliminating air drafts
  • Improves people’s health by preventing the entry of radon gas, suspended particles and other pollutants from outside
Figura 8: Comparativa del nivel de infiltraciones requerido para Passivhaus, CTE y valores típicos para edificios existentes
Figure 10: Air infiltration levels required for Passivhaus compared with Spanish CTE and typical values for existing buildings

An air tightness strategy must always be accompanied by controlled mechanical ventilation, to ensure good air quality and the elimination of moisture and pollutants generated inside the building.

An existing building will typically have an infiltration level of n50 ~10 ach. A certified Passivhaus has an n50 ≤ 0.6 ach. The Spanish CTE Building Regulations, in the 2019 update, establishes a limit for air infiltration of n50 3 ach and 6 ach according to the compacity of the building (Figure 10).

Audits and certification: quality assurance from design to completed building

The certification process and auditing begin in the design phase and conclude when on-site construction is finished. Certification can only be carried out by the Passivhaus Institute or an approved Building Certifier. As an external agent to the project, the certifier verifies that the project complies with the standard and that construction has been completed as planned, accurately reflected in a the PHPP model. The client needs to supply detailed as-built architectural and service drawings, photographic documentation showing the execution of all elements related to energy and air tightness, the final certificate of the Blower Door test, the ventilation system commissioning results, together with a letter signed by the Site Supervisor, indicating that the project has been built as designed.

Passivhaus and health

Although the standard does not specify which materials you use in a building, the PHPP manual explicitly recommends the use of low-emission materials, to reduce VOC’s (volatile organic compounds) in indoor air.

To ensure good air quality, the correct sizing of the ventilation system at design stage is checked. Once installation is completed, the commissioning of the system and the measurement and adjustment of flow rates in all supply and return valves is mandatory.

The goal is to create healthy, comfortable, efficient and resilient buildings, closing the performance gap between projected and real-life performance.

Bibliography

  • [1] EN ISO 13790, Energy performance of buildings – Calculation of energy use for space heating and cooling. This standard has been revised by ISO 52016-1:2017
  • [2] Criteria for the Passivhaus, EnerPHit and PHI Low Energy Building Standard, version 9f. 15.08.2016 1/30. 2016 Passive House Institute.
  • [3] Passive House Institute Summer Temperature Tool, Available at: https://passiv.de/en/05_service/02_tools/02_tools.htm
  • [4] DIN-EN 13829, Thermal performance buildings – Determination of air permeability of buildings – Fan pressurization method. (ISO 9972:1996, modified).